EP3059292A1 - Low- and medium-temperature refrigeration - Google Patents

Abstract

The present invention relates to the use of the binary compositions of 2,3,3,3-tetrafluoropropene and difluoromethane as a heat transfer fluid in compression refrigeration systems, low and medium temperature, with exchangers operating in mode countercurrent or in counter current cross current mode. It also relates to a heat transfer process.

Description

The present invention relates to the use of the binary compositions of 2,3,3,3-tetrafluoropropene and difluoromethane as heat transfer fluids.

The problems posed by ozone depletion potential (ODP) have been addressed in Montreal, where the protocol for reducing the production and use of chlorofluorocarbons (CFCs) has been signed. This protocol has been amended to remove CFCs and extend the regulation to include other products, including hydrochlorofluorocarbons (HCFCs).

The refrigeration and air-conditioning industry has invested heavily in the substitution of these refrigerants and so hydrofluorocarbons (HFCs) have been marketed.

In the automotive industry, the air conditioning systems of vehicles marketed in many countries have moved from a refrigerant to chlorofluorocarbon (CFC-12) to that of hydrofluorocarbon (1,1,1,2 tetrafluoroethane: HFC-134a ), less harmful for the ozone layer. However, in view of the objectives set by the Kyoto Protocol, HFC-134a (GWP = 1300) is considered to have a high warming potential. The contribution to the greenhouse effect of a fluid is quantified by a criterion, the GWP (Global Warming Potentials) which summarizes the warming potential by taking a reference value of 1 for carbon dioxide.

Carbon dioxide being non-toxic, non-flammable and having a very low GWP, has been proposed as a refrigerant for air conditioning systems replacing HFC-134a. However, the use of carbon dioxide has several disadvantages, particularly related to the very high pressure of its implementation as a refrigerant in existing devices and technologies.

Moreover, the R-404A mixture consisting of 44% by weight of pentafluoroethane, 52% by weight of trifluoroethane and 4% by weight of HFC-134a is widely used as a refrigeration fluid of large areas. (supermarket) and in refrigerated transport. This mixture however has a GWP of 3900.

The document JP 4110388 describes the use of hydrofluoropropenes of formula C ₃ H _m F _n , with m, n representing an integer between 1 and 5 inclusive and m + n = 6, as heat transfer fluids, in particular tetrafluoropropene and trifluoropropene .

The document WO2004 / 037913 discloses the use of compositions comprising at least one fluoroalkene having three or four carbon atoms, especially pentafluoropropene and tetrafluoropropene, preferably having a GWP of at most 150, as heat transfer fluids.

The document WO 2006/094303 discloses an azeotropic composition containing 7.4% by weight of 2,3,3,3-tetrafluoropropene (HFO-1234yf) and 92.6% by weight of difluoromethane (HFC-32). This document also discloses azeotropic compositions containing from 1 to 57% by weight of 2,3,3,3-tetrafluoropropene and from 43 to 99% by weight of difluoromethane.

A heat exchanger is a device for transferring heat energy from one fluid to another, without mixing them. The heat flow passes through the exchange surface that separates the fluids. Most of the time this method is used to cool or heat a liquid or gas that can not be cooled or heated directly.

In compression systems, the heat exchange between the refrigerant and the heat sources takes place via the heat transfer fluids. These heat transfer fluids are in the gaseous state (air in conditioned air and direct expansion refrigeration), liquid (water in domestic heat pumps, brine) or diphasic.

• les deux fluides sont disposés parallèlement et vont dans le même sens : mode à co-courant (antiméthodique);
• les deux fluides sont disposés parallèlement mais vont dans le sens opposé: mode à contre-courant (méthodique);
• les deux fluides sont positionnés perpendiculairement : mode à courant croisé. Le courant croisé peut être à tendance co-courant ou contre-courant ;
• un des deux fluides fait un demi-tour dans un conduit plus large, que le deuxième fluide traverse. Cette configuration est comparable à un échangeur à co-courant sur la moitié de la longueur, et pour l'autre moitié à un échangeur à contre courant : mode à tête d'épingle.

There are different modes of transfer:

• the two fluids are arranged in parallel and go in the same direction: co-current mode (antimethodic);
• the two fluids are arranged in parallel but go in the opposite direction: counter-current mode (methodical);
• the two fluids are positioned perpendicularly: cross flow mode. Cross flow may be in co-current or countercurrent trend;
• one of the two fluids makes a half-turn in a wider duct, which the second fluid passes through. This configuration is comparable to a co-current heat exchanger on half the length, and the other half to a counter-current heat exchanger: pinhead mode.

The Applicant has now discovered that binary compositions of 2,3,3,3-tetrafluoropropene and difluoromethane are particularly useful as a heat transfer fluid in compression systems for low and medium temperature refrigeration, with exchangers operating in conventional mode. countercurrent or in counter current cross current mode.

Thus, these compositions can be used as a heat transfer fluid in the refrigeration of refrigerated vehicles, in food preservation and in industry (chemical, food, etc.) with heat exchangers in countercurrent mode or in cross flow mode. counter-current trend.

A first object of the present invention relates to the use of the binary compositions of 2,3,3,3-tetrafluoropropene and difluoromethane as a heat transfer fluid in compression systems for low and medium temperature refrigeration, with exchangers operating in countercurrent mode or in cross current mode with counter current tendency.

Low and medium temperature refrigeration means the range of -45 ° C to -10 ° C at the evaporator.

Preferably, the binary compositions of 2,3,3,3-tetrafluoropropene and difluoromethane contain essentially from 61 to 85% by weight of 2,3,3,3-tetrafluoropropene and from 15 to 39% by weight of difluoromethane.

Advantageously, the binary compositions essentially contain from 70 to 79% by weight of 2,3,3,3-tetrafluoropropene and from 21 to 30% by weight of difluoromethane.

The binary compositions used in the present invention have both a zero ODP and a low GWP. The coefficient of performance (COP: the ratio of cold power to electrical power consumption of a refrigerator) of these binary compositions in heat exchangers in countercurrent mode, is higher than the compositions currently used in low and medium temperature refrigeration. Given the level of pressure in the condenser, it is not necessary to develop new compressors; existing compressors on the market may be suitable.

The binary compositions used in the present invention can replace R-404A and R-407C (ternary mixture containing 52% by weight of HFC-134a, 25% by weight of pentafluoroethane and 23% by weight of difluoromethane) in transfer systems. compression heat with exchangers operating in counter-current or cross-current counter-current mode.

The binary compositions used according to the present invention can be stabilized. The amount of stabilizer is preferably at most 5% by weight based on the binary composition.

As stabilizers, there may be mentioned in particular nitromethane, ascorbic acid, terephthalic acid, azoles such as tolutriazole or benzotriazole, phenol compounds such as tocopherol, hydroquinone, t-butyl hydroquinone, 2 , 6-di-tert-butyl-4-methylphenol, epoxides (optionally fluorinated or perfluorinated alkyl or alkenyl or aromatic) such as n-butyl glycidyl ether, hexanediol diglycidyl ether, allyl glycidyl ether, butylphenylglycidyl ether, phosphites, phosphates, phosphonates, thiols and lactones.

A second subject of the present invention relates to a method of heat transfer in compression systems for low and medium temperature refrigeration, in which the compositions are used. binary 2,3,3,3-tetrafluoropropene and difluoromethane, as defined above, as a refrigerant with exchangers operating in counter-current mode or cross-current mode with countercurrent trend.

The process according to the present invention can be carried out in the presence of lubricants such as mineral oil, alkylbenzene, polyalkylene glycol, polyol ester and polyvinyl ether.

EXPERIMENTAL PART Calculation tools

The RK-Soave equation is used to calculate densities, enthalpies, entropies and vapor-liquid equilibrium data of mixtures. The use of this equation requires knowledge of the properties of the pure bodies used in the mixtures in question and also the interaction coefficients for each binary.

The necessary data for each pure body are:

Boiling temperature, Temperature and critical pressure, the pressure versus temperature curve from the boiling point to the critical point, the saturated liquid and saturated vapor densities as a function of temperature.

HFC-32:

Data on HFC-32 are published in the ASHRAE Handbook 2005 chapter 20 , and are also available under Refrop (Software developed by NIST for the calculation of the properties of refrigerants)

HFO-1234yf:

The data of the temperature-pressure curve of the HFO-1234yf are measured by the static method. The temperature and critical pressure are measured by a C80 calorimeter marketed by Setaram. The saturation densities as a function of temperature are measured by the vibrating tube densimeter technology developed by the laboratories of the Ecole des Mines de Paris.

Binary interaction coefficient of HFC-32 / HFO-1234yf:

The RK-Soave equation uses binary interaction coefficients to represent the behavior of products in mixtures. The coefficients are calculated based on the experimental vapor equilibrium data.

The technique used for liquid vapor equilibrium measurements is the analytical static cell method. The balance cell includes a sapphire tube and is equipped with two electromagnetic ROLSITM samplers. It is immersed in a cryothermostat bath (HUBER HS40). Variable speed rotary field driving magnetic stirring is used to accelerate equilibrium attainment. The analysis of the samples is carried out by chromatography (HP5890 series II) in the gas phase using a katharometer (TCD).

The liquid vapor equilibrium measurements on the HFC-32 / HFO-1234yf binary are carried out for the following isotherms: -10 ° C., 30 ° C. and 70 ° C.

Compression system

Consider a compression system equipped with an evaporator and counterflow condenser, a screw compressor and a pressure reducer.

The system operates with 15 ° C overheating and 5 ° C sub cooling. The minimum temperature difference between the secondary fluid and the refrigerant is considered to be of the order of 5 ° C.

The isentropic efficiency of the compressors is a function of the compression ratio. This yield is calculated according to the following equation: $${\eta }_{\mathit{isen}}=\mathrm{at}-b{\left(\tau -\mathrm{vs}\right)}^2-\frac{d}{\tau -e}$$

For a screw compressor, the constants a, b, c, d and e of equation (1) of the isentropic efficiency are calculated according to the standard data published in the Handbook "Handbook of air conditioning and refrigeration, page 11.52".

The coefficient of performance (COP) is defined as the useful power provided by the system on the power supplied or consumed by the system.

The Lorenz coefficient of performance (COPLorenz) is a benchmark coefficient of performance. It is temperature dependent and is used to compare the COPs of different fluids.

The performance coefficient of Lorenz is defined as follows:

(The temperatures T are in K)

$$T_{\mathit{average}}^{\mathit{condenser}}=T_{\mathit{Entrance}}^{\mathit{condenser}}-T_{\mathit{exit}}^{\mathit{condenser}}$$

$$T_{\mathit{average}}^{\mathit{evaporator}}=T_{\mathit{exit}}^{\mathit{evaporator}}-T_{\mathit{Entrance}}^{\mathit{evaporator}}$$

The Lorenz COP in the case of air conditioning and refrigeration: $$\mathit{COPLorenz}=\frac{T_{\mathit{average}}^{\mathit{evaporator}}}{T_{\mathit{average}}^{\mathit{condenser}}-T_{\mathit{average}}^{\mathit{evaporator}}}$$

The Lorenz COP in the case of heating: $$\mathit{COPLorenz}=\frac{T_{\mathit{average}}^{\mathit{condenser}}}{T_{\mathit{average}}^{\mathit{condenser}}-T_{\mathit{average}}^{\mathit{evaporator}}}$$

For each composition, the performance coefficient of the Lorenz cycle is calculated according to the corresponding temperatures
The% COP / COPLorenz is the ratio of the system COP to the COP of the corresponding Lorenz cycle.

Results low temperature refrigeration mode

In low temperature mode, the compression system operates between a refrigerant inlet temperature at the evaporator of -30 ° C and a refrigerant inlet temperature at the condenser of 40 ° C. The system provides cold at -25 ° C.

The performances of the compositions according to the invention under low temperature operating conditions are given in Table 1. The values of the constituents (HFO-1234yf, HFC-32) for each composition are given in percentage by weight.

Results mode refrigeration medium temperature

In medium temperature mode, the compression system operates between a refrigerant inlet temperature at the evaporator of -15 ° C and a condenser inlet temperature of 35 ° C. The system provides cold at -10 ° C.

The performances of the binary compositions under the medium temperature operating conditions are given in Table 2. The values of the constituents (HFO-1234yf, HFC-32) for each composition are given in percentage by weight.

Claims (8)

Use of a binary composition containing 2,3,3,3-tetrafluoropropene and difluoromethane as a heat transfer fluid in low- and medium-temperature compression refrigeration systems with counter-current or heat exchangers in cross-current mode with counter current trend. Use according to Claim 1, characterized in that the composition contains essentially 61 to 85% by weight of 2,3,3,3-tetrafluoropropene and 15 to 39% by weight of difluoromethane. Use according to Claim 1, characterized in that the composition contains essentially 70 to 79% by weight of 2,3,3,3-tetrafluoropropene and 21 to 30% by weight of difluoromethane. A heat transfer process in which a binary composition containing 2,3,3,3-tetrafluoropropene and difluoromethane is used as a refrigerant in low and medium temperature compression refrigeration systems with heat exchangers operating in counter mode. -current or cross-current mode with counter current trend. Process according to Claim 4, characterized in that the composition essentially contains from 61 to 85% by weight of 2,3,3,3-tetrafluoropropene and from 15 to 39% by weight of difluoromethane. Process according to Claim 4, characterized in that the composition contains essentially 70 to 79% by weight of 2,3,3,3-tetrafluoropropene and 21 to 30% by weight of the difluoromethane. Process according to Claims 4 to 6, characterized in that the binary composition is stabilized. Process according to any one of Claims 4 to 7, characterized in that it is carried out in the presence of a lubricant.